Electric heater



FIG. 1 is a perspective view of an ornamental design for an electric heater according to the present invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a right side view thereof. 

The ornamental design for an electric heater, as shown. 